1. Field of the Invention
The present invention relates to a barrel for aligning optical axes of a plurality of lenses and, particularly, to a barrel capable of automatically aligning respective optical axes of a plurality of lenses.
2. Description of Related Art
Presently, with the development of optical imaging technology, digital cameras, video cameras, and portable electronic devices (e.g., mobile phones, PDAs (personal digital assistants), and portable computers) incorporating cameras are now widely used. More and more consumers desire a higher image quality produced using such camera modules.
A typical camera module generally includes a lens module. The lens module is coupled with an image sensor, such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS), so as to capture images. Generally, the lens module includes a holder and a barrel threadedly received in the holder. A plurality of lenses and spacers are arranged in alternating fashion in the barrel. In addition, an infrared-cut filter that blocks light in the infrared spectrum often is also fitted in the lens module to prevent interference. Before the acceptable lens module can be sold, imaging quality of the lens module, after assembly thereof, must be ensured. Accordingly, concentricity of the lenses must be detected in order to ensure of the quality of the camera. How, consistently, to align the respective optical axes of the plurality of lenses in the barrel has proven a critical problem for operators/assemblers.
Generally, a tolerance between a diameter of the lens and an internal diameter of the barrel is considered a vital factor in controlling deviation in a position of an optical axis of the lens. Conventionally, the lenses are installed, in a desired order, into the barrel by operators or a special machine. During assembly of the lenses, the position of the respective optical axis of each lens cannot be precisely controlled due to clearance between the lens and the barrel. Therefore, a deviation between the respective optical axes can result, and, as a result, an image resolution of the lens module can suffer to some degree. Referring to FIG. 5, after a first lens 12, a second lens 14, and a third lens 16 have been installed into a barrel 10, there still is clearance between the first, second, and third lenses 12, 14, 16 and the barrel 10. As a result, the optical axes of the first, second, and third lenses 12, 14, 16 are non-concentric (i.e., not aligned). Thus, after the lens module has been installed, image resolution and the ratio of acceptable products tend to be dramatically reduced. Given that unfavorable ratio, the effective manufacturing cost is correspondingly increased (i.e., to achieve a sufficient number of acceptable units).
What is needed, therefore, is a barrel for automatically aligning the respective optical axes of a plurality of lenses to thereby overcome the above-mentioned disadvantages.